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PowerPoint® Lecture Slides
prepared by
Betsy C. Brantley
Valencia College
CHAPTER
9
The Senses
© 2013 Pearson Education, Inc.
Chapter 9 Learning Outcomes
• Section 1: The General Senses
• 9.1
• List the types of sensory receptors found in the skin, and specify
the functions of each.
• 9.2
• Explain the roles of baroreceptors and chemoreceptors in
homeostasis.
• Section 2: The Special Senses
• 9.3
• Describe the sensory organs of smell and trace the olfactory
pathways to their destination in the cerebrum, and describe the
sensory organs and cranial nerves involved with gustation.
© 2013 Pearson Education, Inc.
Chapter 9 Learning Outcomes
• 9.4
• Describe the structures of the external, middle, and internal ear,
and explain how they function.
• 9.5
• Describe the structures and functions of the bony labyrinth and
membranous labyrinth.
• 9.6
• Describe the functions of hair cells in the semicircular ducts,
utricle, and saccule, and explain their role in responding to
gravity and linear acceleration.
• 9.7
• Describe the cochlear duct and spiral organ, and describe the
structure and functions of the spiral organ.
© 2013 Pearson Education, Inc.
Chapter 9 Learning Outcomes
• 9.8
• Describe the anatomical and physiological basis for the
sensations of pitch and volume related to hearing.
• 9.9
• Identify the accessory structures of the eye and explain their
functions, and define conjunctivitis.
• 9.10
• Describe the layers of the eye wall and the anterior and
posterior eye cavities, and state the names and functions of the
extrinsic eye muscles.
• 9.11
• Explain how light is directed to the fovea of the retina.
• 9.12
• Describe the process by which images are focused on the
retina.
© 2013 Pearson Education, Inc.
Chapter 9 Learning Outcomes
• 9.13
• Explain the structure and function of the retina's layers, describe
the distribution of rods and cones, and discuss the role of
photoreceptors in visual acuity.
• 9.14
• Explain photoreception, describe the structure of
photoreceptors, explain how visual pigments are activated, and
describe how we are able to distinguish colors.
• 9.15
• Explain how the visual pathways distribute information to their
destinations in the brain.
• 9.16
• CLINICAL MODULE Describe various accommodation
problems associated with the cornea, lens, or shape of the eye.
© 2013 Pearson Education, Inc.
Chapter 9 Learning Outcomes
• 9.17
• CLINICAL MODULE Describe age-related disorders of olfaction,
gustation, vision, equilibrium, and hearing.
© 2013 Pearson Education, Inc.
General Senses (Section 1)
• Sensitivity to temperature, pain, touch, pressure, vibration,
and proprioception
• Picked up by sensory receptors
• Specialized cells or cell processes
• Simplest – dendrites of sensory neurons (free nerve endings)
• Stimulated by many different stimuli (chemical, pressure,
temperature)
• Little receptor specificity
© 2013 Pearson Education, Inc.
Sensory receptors
Free
nerve
endings
© 2013 Pearson Education, Inc.
Figure 9 Section 1 1 1
General Sensory Receptors – Classification
(Section 1)
• Classified according to nature of primary stimulus
• Nociceptors
• Pain receptors
• Large receptive fields and broad sensitivity
• Type A and type C fibers (axons) carry pain sensation
• Thermoreceptors (temperature receptors)
• Located in dermis, skeletal muscles, liver, hypothalamus
• Cold receptors 3–4 times more numerous than warm
receptors
© 2013 Pearson Education, Inc.
General Sensory Receptors – Classification
(Section 1)
• Mechanoreceptors
• Sensitive to plasma membrane change (stretching,
compression, twisting, or other mechanical distortion)
• Proprioceptors – monitor positions of joints and muscles
• Baroreceptors – detect pressure changes in walls of blood
vessels and portions of system tracts
• Tactile receptors – provide touch, pressure, vibration
sensation
• Chemoreceptors
• Respond to substances dissolved in body fluids
© 2013 Pearson Education, Inc.
Functional classification of general sensory receptors
A Functional Classification of General Sensory Receptors
Nociceptors
Thermoreceptors
Mechanoreceptors
Proprioceptors
© 2013 Pearson Education, Inc.
Baroreceptors
Chemoreceptors
Tactile
receptors
Figure 9 Section 1 1 2
General Sensory Receptors in Skin (9.1)
• Greatest diversity of general sensory receptors
• Tactile sensitivity can be altered by infection,
disease, or damage to sensory neurons or
pathways
• Tactile responses used for diagnosis
• Sensory loss along dermatome boundary can help
identify affected spinal nerve or nerves
© 2013 Pearson Education, Inc.
Tactile Corpuscles
General sensory receptors in the skin
Hair
Free Nerve Endings
Capsule
Dendrites
Tactile
corpuscle
Dermis
Afferent
fiber
Lamellated Corpuscles
Layers of
collagen
fibers
separated
by fluid
Free nerve
endings
Sensory
nerve
Dendrite
Dermis
Root Hair Plexus
Hair shaft
Root hair
plexus
Ruffini Corpuscles
Sensory nerves
Capsule
Dendrites
Afferent
fiber
Tactile Discs
Specialized
epithelial cells
Tactile disc
© 2013 Pearson Education, Inc.
Figure 9.1
Skin Receptors – Free Nerve Endings (9.1)
• Branching tips of sensory neurons
• Not protected; nonspecific
• Respond to tactile, pain, and temperature stimuli
• Most common receptors in skin
© 2013 Pearson Education, Inc.
Free nerve endings
Hair
Free Nerve Endings
Free nerve
endings
Sensory
nerve
Sensory nerves
© 2013 Pearson Education, Inc.
Figure 9.1
Skin Receptors – Root Hair Plexus (9.1)
• Monitor distortions and movements across body
surface
• Hair displaced, movement of follicle distorts
sensory dendrites
• Produces action potentials (messages)
© 2013 Pearson Education, Inc.
Root hair plexus
Hair
Root Hair Plexus
Hair shaft
Root hair
plexus
© 2013 Pearson Education, Inc.
Sensory nerves
Figure 9.1
Skin Receptors – Tactile Discs (9.1)
• Fine touch and pressure receptors
• Dendrites of afferent fiber in contact with
specialized epithelial cells in epidermis
© 2013 Pearson Education, Inc.
Tactile discs
Hair
Sensory
nerves
Tactile Discs
Specialized
epithelial cells
Tactile disc
© 2013 Pearson Education, Inc.
Figure 9.1
Skin Receptors - Tactile Corpuscles (9.1)
• Also called Meissner corpuscles
• Provide sensations of fine touch and pressure and lowfrequency vibration
• Adapt to stimulation within a second
• Most abundant in eyelids, lips, fingertips, nipples, external
genitalia
• Coiled and interwoven dendrites surrounded by modified
Schwann cell
• Fibrous capsule around entire complex anchors within dermis
© 2013 Pearson Education, Inc.
Tactile corpuscles
Hair
Tactile Corpuscles
Capsule
Dendrites
Tactile
corpuscle
Dermis
Afferent
fiber
Sensory nerves
© 2013 Pearson Education, Inc.
Figure 9.1
Skin Receptors - Lamellated Corpuscles (9.1)
• Also called pacinian corpuscles
• Sensitive to deep pressure
• Most sensitive to pulsing or high-frequency vibration
• Single dendrite wrapped in concentric layers of collagen
fibers and specialized fibroblasts
• Located in dermis, mammary glands, external genitalia
• Also found in mesenteries, pancreas, walls of urethra
and urinary bladder
© 2013 Pearson Education, Inc.
Lamellated corpuscles
Hair
Lamellated Corpuscles
Layers of
collagen
fibers
separated
by fluid
Dendrite
Dermis
Sensory nerves
© 2013 Pearson Education, Inc.
Figure 9.1
Skin Receptors – Ruffini Corpuscles (9.1)
• Sensitive to pressure and distortion of reticular (deep)
dermis
• Little, if any, adaptation (reduction in sensitivity to constant
stimulus)
• Network of dendrites intertwined with collagen fibers
• Surrounded by capsule
• Distortion of surrounding dermis tugs/twists capsule fibers
• Dendrites in turn stretched or compressed
• Sends message along afferent fiber
© 2013 Pearson Education, Inc.
Ruffini corpuscles
Hair
Sensory nerves
Ruffini Corpuscles
Capsule
Dendrites
Afferent
fiber
© 2013 Pearson Education, Inc.
Figure 9.1
Module 9.1 Review
a. Identify the six types of tactile receptors located
in the skin, and describe their sensitivities.
b. Which types of tactile receptors are located only
in the dermis?
c. Which is likely to be more sensitive to continuous
deep pressure: a lamellated corpuscle or a
Ruffini corpuscle?
© 2013 Pearson Education, Inc.
Baroreceptors (9.2)
• Stretch receptors that monitor changes in pressure
• Free nerve endings branching within elastic
tissues
• Pressure changes cause stretch or recoil of elastic
tissues
• Change in tissue distorts receptor's branches
• Structural distortion alters rate of action-potential
generation
© 2013 Pearson Education, Inc.
Baroreceptor Locations (9.2)
• Carotid sinus and aortic sinus – monitor blood pressure
• Information sent plays role in regulating cardiac function and
adjusting blood flow
• Lungs – monitor degree of lung expansion
• Information sent to respiratory centers to control breathing
rate/rhythm
• Colon – monitor fecal matter volume; trigger defecation
• Digestive tract – monitor volume; trigger reflex movement
• Urinary bladder wall – monitor volume; trigger urination
© 2013 Pearson Education, Inc.
Locations of baroreceptors in the body
Baroreceptors of Carotid
Sinus and Aortic Sinus
Baroreceptors of
Digestive Tract
Baroreceptors
of Bladder Wall
© 2013 Pearson Education, Inc.
Baroreceptors of Lungs
Baroreceptors of Colon
Figure 9.2 1 1
Chemoreceptors (9.2)
• Detect small changes in concentrations of specific
chemicals or compounds
• Play role in reflexive control of respiration and
cardiovascular function
1. Within medulla oblongata
• Monitor pH and carbon dioxide levels in cerebrospinal
fluid
2. In carotid bodies
• Monitor pH, carbon dioxide, and oxygen levels in blood
3. In aortic bodies
• Monitor pH, carbon dioxide, and oxygen levels in blood
© 2013 Pearson Education, Inc.
Chemoreceptors in Respiratory
Centers in the Medulla
Oblongata
Locations of chemoreceptors
Chemoreceptors of Carotid
Bodies
Chemoreceptors of Aortic
Bodies
Trigger reflexive
adjustments in
depth and rate
of respiration
Cranial
nerve IX
Cranial
nerve X
Trigger reflexive
adjustments in
respiratory and
cardiovascular
activity
Branch of cranial nerve IX
Internal carotid
External carotid
Carotid body
Carotid sinus
Common carotid
© 2013 Pearson Education, Inc.
Figure 9.2 1 2 – 3
Module 9.2 Review
a. Define baroreceptor and chemoreceptor.
b. Which type of receptor is sensitive to changes in
blood pH?
c. Where are baroreceptors located within the
body?
© 2013 Pearson Education, Inc.
Special Senses (Section 2)
•
Receptors more structurally complex than receptors for
general senses
•
Located in sense organs with protective surrounding
tissue
•
Information distributed to specific areas in cerebral cortex
•
Five special senses
1. Olfaction (smell)
2. Vision (sight)
3. Gustation (taste)
4. Equilibrium (balance)
5. Hearing
© 2013 Pearson Education, Inc.
Olfaction and Taste Receptors (Section 2)
• Olfaction sensory receptors
• Modified neurons
• Gustation sensory receptors
• Specialized receptor cells communicating with sensory
neurons
• Both olfaction and gustation
• Sensory receptors in epithelia
• Exposed to environment
• Information routed directly to CNS for processing
© 2013 Pearson Education, Inc.
Olfactory and gustatory sensory receptors
Taste
receptor
Olfactory
receptor
© 2013 Pearson Education, Inc.
Figure 9 Section 2 1 1
Hearing and Equilibrium Receptors (Section 2)
• Sensory receptors protected from external environment in
internal ear
• Sensory information integrated and organized before
forwarded to CNS
• Receptors called hair cells
• Free surfaces are covered with processes similar to microvilli
• Mechanoreceptors are surrounded by supporting cells and
monitored by dendrites of sensory neurons
• External force distorts hair cell plasma membrane, altering
rate of chemical transmitter release to sensory neuron
© 2013 Pearson Education, Inc.
Receptors for hearing and equilibrium
Internal ear
Displacement
in this direction
stimulates hair cell
Displacement
in this direction
inhibits hair cell
Hair cell
Dendrite of
sensory neuron
Supporting cell
© 2013 Pearson Education, Inc.
Figure 9 Section 2 1 2 – 3
Sense of Smell (9.3)
• Olfaction (sense of smell)
• Provided by paired olfactory organs
• Located in nasal cavity
• Cover inferior surface of cribriform plate, superior portion
perpendicular plate, superior nasal conchae
• Odorants
• Dissolved chemicals that stimulate olfactory receptors
• Small, organic molecules
• As few as four molecules can activate olfactory receptor
© 2013 Pearson Education, Inc.
Olfactory Pathway (9.3)
1. Sensory neurons stimulated by chemicals in the air
2. Axons leaving olfactory epithelium collect into 20 or more
bundles; penetrate cribriform plate of ethmoid bone
3. These axons communicate with next neurons in olfactory
bulb (superior to cribriform plate)
4. Axons leaving olfactory bulb form olfactory tract
5. Information distributed to olfactory cortex, limbic system,
and hypothalamus
6. Strong emotional response and memories associated with
smell
© 2013 Pearson Education, Inc.
Olfactory pathway to the cerebrum
Olfactory Pathway to the Cerebrum
Olfactory
Olfactory nerve Olfactory
epithelium
fibers (NI)
bulb
Olfactory
tract
Central nervous
system
Stem cell
Supporting cell
Olfactory
receptor
Cribriform
plate of
ethmoid
Olfactory
epithelium
of the right
olfactory
organ
Superior
nasal
concha
Odorants
© 2013 Pearson Education, Inc.
Figure 9.3 2 1
Sense of Taste (9.3)
• Gustation
• Provides information about foods and liquids we consume
• Taste receptors located on superior surface of tongue,
adjacent portions of pharynx and larynx
• Lingual papillae – epithelial projections on tongue
1. Circumvallate papillae – large, shaped like pencil eraser
tip, surrounded by deep epithelial folds; each papilla
contains up to 100 taste buds
2. Fungiform papillae – also contain taste buds
3. Filiform papillae
© 2013 Pearson Education, Inc.
Cranial Nerves and Taste (9.3)
• Taste information carried on cranial nerves
• Vagus nerve (X) – from taste buds on surface of epiglottis
• Glossopharyngeal nerve (IX) – from posterior 1/3 of tongue
• Facial nerve (VII) – from anterior 2/3 of tongue
• Taste sensations
• Four primary – sweet, salty, sour, bitter
• Umami – detected by receptors sensitive to amino acids,
small peptides, nucleotides; taste of beef broth or Parmesan
cheese
• Water receptors – concentrated in pharynx, provide
information to hypothalamus for water balance regulation
© 2013 Pearson Education, Inc.
Taste receptors
Circumvallate Papillae
Cranial Nerves
Carrying Taste
Information
Circumvallate
papillae
Epiglottis
Water
receptors
(pharynx)
Vagus nerve
Glossopharyngeal
nerve
Taste
buds
Umami
Facial nerve
Sour
Bitter
Salty
Sweet
Supporting
cell
Taste cell
Stem cell
Diagrammatic view of a
taste bud
Filiform Papillae
© 2013 Pearson Education, Inc.
Fungiform Papillae
Figure 9.3 2 2
Module 9.3 Review
a. Describe olfaction and its receptors.
b. Describe gustation and its receptors.
c. Trace the olfactory pathway, beginning at the
olfactory epithelium.
© 2013 Pearson Education, Inc.
External Ear (9.4)
• Visible portion of ear
• Collects and directs sound waves toward middle ear
• Elastic cartilage gives auricle flexibility
• External acoustic meatus
• Passageway within temporal bone
• Lined with small hairs and ceruminous glands that secrete
cerumen (earwax)
• Cerumen slows microorganism growth, reducing chances for
external ear infection
• Cerumen and hairs prevent foreign objects and insects from
reaching internal structures
© 2013 Pearson Education, Inc.
Middle Ear (9.4)
• Also called tympanic cavity
• Air-filled chamber
• Separated from external acoustic meatus by tympanic membrane
or eardrum
• Thin, semitransparent sheet
• Connected to pharynx by auditory tube or Eustachian tube
• Permits pressure equalization on either side of tympanic
membrane
• Also allows microorganisms to travel from nasopharynx to
middle ear, potentially causing infection called otitis media
• Contains auditory ossicles
© 2013 Pearson Education, Inc.
Internal Ear (9.4)
• Contains sensory organs for hearing and
equilibrium
• Receives amplified sound waves from middle ear
• Superficial contours formed by layer of dense
bone called bony labyrinth
© 2013 Pearson Education, Inc.
Structures in the ear
External Ear
Middle Ear
Auricle
Auditory ossicles
Auricle
Internal Ear
Semicircular
canals
Temporal bone
Facial nerve ( VII)
Vestibulocochlear
nerve ( VIII)
Bony labyrinth
Tympanic
cavity
Tympanic
membrane
External acoustic meatus
© 2013 Pearson Education, Inc.
To
nasopharynx
Auditory tube
Figure 9.4 1 1
Auditory Ossicles (9.4)
• Three auditory ossicles conduct and amplify vibrations to
internal ear
1. Malleus – attaches to tympanic membrane
2. Incus – attaches malleus to stapes
3. Stapes – attaches incus to oval window, an opening in bone
surrounding internal ear
• Located in middle ear
• Articulations between are smallest synovial joints in body
• Small skeletal muscles that insert on malleus and stapes
contract to reduce amount of vibration to protect tympanic
membrane
© 2013 Pearson Education, Inc.
Auditory ossicles location
Auditory Ossicles
Malleus
Incus
Stapes
Temporal bone
(petrous part)
Connections to
mastoid air cells
Oval
window
Stabilizing
ligament
Branch of facial
nerve VII (cut)
Muscles of the Middle Ear
External acoustic
meatus
Tympanic cavity
(middle ear)
Auditory tube
Round window
Tympanic membrane
© 2013 Pearson Education, Inc.
Figure 9.4 2 2
Module 9.4 Review
a. Name the three tiny bones located in the middle
ear.
b. What is the function of the auditory tube?
c. Why are external ear infections relatively
uncommon?
© 2013 Pearson Education, Inc.
Bony Labyrinth (9.5)
• Internal ear divided into bony and membranous labyrinths
• Bony labyrinth
• Shell of dense bone
• Surrounds and protects membranous labyrinth
• Composed of three parts
1. Semicircular canals
2. Vestibule
3. Cochlea
• Perilymph – flows between bony and membranous labyrinths
© 2013 Pearson Education, Inc.
Internal ear structures
Bony Labyrinth
Semicircular canals Vestibule Cochlea
Membranous Labyrinth
Receptor
areas
Semicircular ducts
Utricle and saccule
Cochlear duct
Bony labyrinth
Perilymph
Membranous labyrinth
Endolymph
© 2013 Pearson Education, Inc.
KEY
Membranous
labyrinth
Bony labyrinth
Figure 9.5
1 – 2
Membranous Labyrinth (9.5)
• Collection of fluid-filled tubes and chambers
• Houses receptors for equilibrium and hearing
• Filled with endolymph; surrounded by perilymph
• Composed of:
1. Vestibular complex
• Semicircular ducts – within semicircular canals, monitor
rotational movements in three different planes
• Vestibule containing utricle and saccule – contain receptors
sensitive to gravity and linear acceleration
2. Cochlear duct – contained within cochlea, forms spiral-like snail
shell, involved in hearing
© 2013 Pearson Education, Inc.
Concept map for membranous labyrinth with illustration
Membranous Labyrinth
Vestibular Complex (equilibrium)
Semicircular
Ducts
© 2013 Pearson Education, Inc.
Cochlear Duct (hearing)
Utricle and
Saccule
Figure 9.5 3 3
Module 9.5 Review
a. Identify the components of the bony labyrinth.
b. What separates the membranous labyrinth from
the bony labyrinth?
c. Explain the regional differences in the
sensitivities of the various receptor complexes in
the membranous labyrinth.
© 2013 Pearson Education, Inc.
Semicircular Ducts (9.6)
• Contains hair cells that respond to rotation
• Three ducts
1. Anterior
2. Posterior
3. Lateral
• Each duct has an ampulla (expanded region)
• Receptors in specific region of ampulla called crista
ampullaris
• Processes of hair cells embedded in cupula (flexible,
elastic, gelatinous structure)
© 2013 Pearson Education, Inc.
Crista ampullaris location
Semicircular Ducts
Anterior
Posterior
Lateral
Ampulla
Utricle
Cupula
Ampulla filled
with endolymph
Hair cells
Crista
ampullaris
Supporting cells
Sensory nerve
© 2013 Pearson Education, Inc.
Figure 9.6 1 1
Endolymph Movement (9.6)
• Cupula floats in endolymph above crista ampullaris
• Rotation of head causes:
• Movement of endolymph
• Movement of cupula to side
• Distortion of receptor processes
• Movement in one direction stimulates hair cells
• Movement in opposite direction inhibits hair cells
• Stopping rotational movement stops endolymph movement
and cupula returns to normal position
© 2013 Pearson Education, Inc.
Change in endolymph movement with head rotation
Direction of
duct rotation
Direction of relative
endolymph movement
Direction of
duct rotation
Semicircular duct
Ampulla
© 2013 Pearson Education, Inc.
At rest
Figure 9.6 2 2
Rotational Planes (9.6)
• Three semicircular ducts lie in three rotational
planes
• Each responds to one rotational movement
• Horizontal rotation (shaking head "no") stimulates
receptors in lateral semicircular duct
• Vertical rotation (nodding "yes") stimulates receptors in
anterior semicircular duct
• Tilting head side to side stimulates receptors in posterior
semicircular duct
© 2013 Pearson Education, Inc.
Rotational planes of semicircular canals
Anterior semicircular
duct for "yes"
Posterior semicircular
duct for tilting head to the side
© 2013 Pearson Education, Inc.
Figure 9.6 3 3
Utricle and Saccule Equilibrium Sensation (9.6)
• Sensory structure in utricle and saccule is a
macula
• Hair cell processes embedded in gelatinous otolithic
membrane
• Surface of membrane packed with calcium carbonate
crystals called otoliths (ear stones)
• Utricle sensitive to changes in horizontal
movement
• Saccule sensitive to changes in vertical movement
© 2013 Pearson Education, Inc.
Structures in the macula
Utricle
Endolymphatic
sac
Endolymphatic
duct
Saccule
Gelatinous layer
forming otolithic
membrane
Otoliths
Nerve fibers
Hair cells
© 2013 Pearson Education, Inc.
Figure 9.6
4 – 5
Changing Head Position (9.6)
• Head upright
• Otoliths on top of otolithic membrane
• Weight presses on macular surface, pushing hair cell processes
down
• Head tilted
• Gravity pulls on otoliths, shifting to side
• Otolith movement distorts hair cell processes stimulating receptors
• Perception of linear acceleration – otoliths lag behind, giving effect
of tilting head
© 2013 Pearson Education, Inc.
Otolithic membrane movement with change in position
Gravity
Gravity
Receptor
output
increases
© 2013 Pearson Education, Inc.
Otolith
moves
“downhill,”
distorting hair
cell processes
Figure 9.6 6 6
Module 9.6 Review
a. Define otoliths.
b. Cite the function of receptors in the saccule and
utricle.
c. Damage to the cupula of the lateral semicircular
duct would interfere with what perception?
© 2013 Pearson Education, Inc.
Cochlear Duct (9.7)
• Long, coiled tube suspended between two chambers filled
with perilymph
1. Scala vestibuli
2. Scala tympani
• Bony labyrinth encases all three ducts except at oval
window (base of scala vestibuli) and round window (base
of scala tympani)
• Hair cells of cochlear duct in structure called spiral organ,
or organ of Corti, which runs length of cochlea
© 2013 Pearson Education, Inc.
Cochlear structures
Scala vestibuli
Round window
Stapes at oval
window
Cochlear duct
Scala tympani
From oval
window
Cochlear Vestibular
branch
branch
Vestibulocochlear
nerve (VIII)
Vestibular membrane
Basilar membrane
Scala vestibuli
Spiral organ
Cochlear duct
Scala tympani
Temporal bone
(petrous part)
To round
window
© 2013 Pearson Education, Inc.
Cochlear nerve
Vestibulocochlear nerve (VIII)
Semicircular
canals
KEY
From oval window
to tip of spiral
From tip of spiral
to round window
Figure 9.7
11 – 22
Sectional view of cochlear spiral
Sectional view of the cochler spiral
© 2013 Pearson Education, Inc.
LM x 200
Figure 9.7
22
Spiral Organ (9.7)
• Cochlear duct separated:
• From scala vestibuli by vestibular membrane
• From scala tympani by basilar membrane
• Spiral organ located in cochlear duct on basilar membrane
• Processes of spiral organ hair cells in contact with
overlying tectorial membrane
• Sensory neurons monitor hair cell movement
• Axons of these sensory neurons form cochlear branch of
vestibulocochlear nerve (VIII)
© 2013 Pearson Education, Inc.
Details of cochlear structures
Bony cochlear wall
Scala vestibuli
Vestibular membrane
Cochlear duct
Basilar membrane
Cell bodies of sensory
neurons
Scala tympani
Cochlear branch of
vestibulocochlearnerve
Spiral organ
Tectorial membrane
Outer
hair cell
Basilar
membrane
© 2013 Pearson Education, Inc.
Inner hair
cell
Nerve
fibers
Figure 9.7
33 – 44
Pressure Wave (9.7)
• Sound waves at tympanic membrane trigger
pressure changes in perilymph in cochlea
• Basilar membrane bounces up and down in
response to pressure changes
• Hair cell processes pushed against tectorial
membrane and distorted
• More movement means more hair cells and more
rows of hair cells stimulated
© 2013 Pearson Education, Inc.
Changes in hair cell movement with pressure wave
Distortion of hair
cell processes
At rest
© 2013 Pearson Education, Inc.
Pressure wave
in perilymph
Figure 9.7
44
Module 9.7 Review
a. Where is the spiral organ located?
b. Name the fluids found within the scala vestibuli,
scala tympani, and cochlear duct.
c. Identify the structures visible in the light
microscope of the cochlear spiral in sectional
view.
© 2013 Pearson Education, Inc.
Hearing (9.8)
• Perception of sound
• Sound
• Waves of pressure conducted through a medium
• In each wave, area of compressed molecules and area
of molecules farther apart
• Distance between adjacent wave crests (or troughs) is
wavelength
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Sound waves are waves of pressure conducted through a medium
Wavelength
Air molecules
Tuning fork
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Tympanic
membrane
Figure 9.8 1 1
Sound Frequency (9.8)
• Frequency
• Number of waves (cycles) passing a fixed point in a given
time
• Frequency of sound measured in cycles per second (cps) or
hertz (Hz)
• Pitch of sound is really frequency
• Sound travels at same speed, so higher frequency means
shorter wavelengths
• High frequency sound = high pitch; 15,000 Hz or more
• Very low frequency sound = low pitch; 100 Hz or less
© 2013 Pearson Education, Inc.
Frequency and amplitude of sound waves
Sound energy arriving at
tympanic membrane
Wavelength
Amplitude
1 wavelength
0
© 2013 Pearson Education, Inc.
Time (sec)
Figure 9.8 2 2
Volume or Intensity (9.8)
• Amplitude of sound wave determined by amount
of energy carried
• Amount of energy in sound waves is intensity
• Louder sounds have greater energy so higher
amplitudes
• Measured in decibels (dB)
© 2013 Pearson Education, Inc.
© 2013 Pearson Education, Inc.
Figure 9.8 3 3
Pitch Determination (9.8)
• Sound waves striking a flexible object make it vibrate
• Vibration to same frequency of sound waves is resonance
• Tympanic membrane resonates to sound waves
• Movement of tympanic membrane causes pressure waves
in cochlea
• Basilar membrane more flexible in some regions,
resonates to different frequencies at different locations
• Location of vibration interpreted as pitch
• Number of stimulated hair cells interpreted as volume
© 2013 Pearson Education, Inc.
Location of movement produced by sound of different frequencies
Cochlea
Stapes
at oval
window
16,000 Hz
Round
window
Less flexible
6000 Hz
Basilar membrane
1000 Hz
More flexible
This diagram shows the location where movement
of the basilar membrane is produced by sound waves
of different frequencies
© 2013 Pearson Education, Inc.
Figure 9.8 4 4
Events involved in hearing
Events Involved in Hearing
Sound waves
arrive at the
tympanic
membrane.
Movement of
the tympanic
membrane causes
displacement of the
auditory ossicles.
1
2
Movement of the
stapes at the oval
window establishes
pressure waves in
the perilymph of the
scala vestibuli.
3
The pressure
waves distort the
basilar membrane
on their way to the
round window of
the scala tympani.
4
Vibration of the
basilar membrane
causes vibration of
hair cells against the
tectorialmembrane.
5
Information about the
region and the intensity
of stimulation is relayed
to the CNS over the
cochlear branch of
cranial nerve VIII.
6
Tympanic duct
Basilar membrane
Cochlear duct
Vestibular membrane
Movement
of sound
waves
Vestibular duct
Tympanic
membrane
© 2013 Pearson Education, Inc.
Round
window
Figure 9.8 5 5
Module 9.8 Review
a. Define decibel.
b. Beginning at the external acoustic meatus, list the
events in hearing.
c. How would sound perception be affected if the
round window could not bulge out as a result of
increased perilymph pressure?
© 2013 Pearson Education, Inc.
Eyelids and Eyelashes (9.9)
• Eyelash
• Helps prevent foreign matter from reaching eye surface
• Eyelid or palpebra
• Continuation of skin
• Blinking of eyelids keeps eye surface lubricated and removes
dust and debris, protects eye surface
• Palpebral fissure is gap separating upper and lower eyelids
• Connected by medial and lateral canthus
• Lacrimal caruncle
• Location of glands producing thick secretions
© 2013 Pearson Education, Inc.
Accessory structures of the eye
Eyelids and Eyelashes
Eyelashes
Cornea
Eyelid or palpebra
Medial canthus
Lateral canthus
Palpebral fissure
Pupil
Lacrimal caruncle
© 2013 Pearson Education, Inc.
Figure 9.9 1 1
Conjunctiva (9.9)
• Epithelium covering inner surfaces of eyelids and outer
surface of eye
• Mucous membrane covered by specialized stratified
squamous epithelium
• Continuous with epithelium covering surface of cornea
(transparent area on anterior surface)
• Tarsal glands or Meibomian glands
• Modified sebaceous glands on inner margin of each eyelid
• Secrete lipid-rich product keeping eyelids from sticking
together
© 2013 Pearson Education, Inc.
Conjunctiva of the eye
Tarsal glands
Conjunctiva
Conjunctiva
© 2013 Pearson Education, Inc.
Figure 9.9 2 2
Tears (9.9)
• Produced by lacrimal gland
• Reduce friction
• Remove debris
• Prevent bacterial infection (contain antibacterial
enzyme lysozyme and antibodies)
• Provide nutrients and oxygen to conjunctival
epithelium
© 2013 Pearson Education, Inc.
Lacrimal Apparatus (9.9)
1. Produces, distributes, and removes tears
2. Lacrimal gland or tear gland with associated ducts
• Almond-shaped gland produces 1 mL tears per day
• Tear ducts deliver tears from lacrimal gland to space behind
upper eyelid
• Lacrimal puncta – small pores drain lacrimal lake (where
tears collect)
3. Paired lacrimal canaliculi – small canals connect lacrimal
puncta to lacrimal sac
4. Lacrimal sac – nestles in lacrimal sulcus of orbit
5. Nasolacrimal duct – carries tears from lacrimal sac to
inferior meatus in nasal cavity
© 2013 Pearson Education, Inc.
Lacrimal apparatus
Components of the
Lacrimal Apparatus
Lacrimal gland
Superior
rectus
muscle
Tear ducts
Lacrimal puncta
Upper eyelid
Lower eyelid
Orbital fat layer
Lacrimal canaliculi
Lacrimal sac
Nasolacrimal duct
Inferior rectus
muscle
Inferior oblique
muscle
© 2013 Pearson Education, Inc.
Inferior meatus
Figure 9.9 3 3
Conjunctivitis (9.9)
• Also called pinkeye
• From damage to and irritation of conjunctival surface
• Redness from dilated blood vessels deep to conjunctival
epithelium
• Caused by:
• Pathogenic infection
• Physical, allergic, or chemical irritation
© 2013 Pearson Education, Inc.
Conjunctivitis
© 2013 Pearson Education, Inc.
Figure 9.9 4 4
Module 9.9 Review
a. List the accessory structures associated with the
eye.
b. Explain conjunctivitis.
c. Which layer of the eye would be the first affected
by inadequate tear production?
© 2013 Pearson Education, Inc.
Wall of the Eye – Fibrous Layer (9.10)
• Three layers of eye wall (fibrous, vascular, neural)
• Fibrous layer – outermost layer
• Consists of continuous components cornea and sclera
• Border between is corneal limbus
• Functions:
1. Provides mechanical support and physical protection
2. Attachment site for extrinsic eye muscles
3. Contains cornea, which allows passage of light and aids
in focusing process
© 2013 Pearson Education, Inc.
Wall of Eye – Vascular Layer (9.10)
1. Provides route for blood vessels and lymphatics to eye
• Choroid – contains extensive capillary networks
2. Regulates amount of light entering eye
• Iris – contains blood vessels, pigment cells, smooth muscle;
controls pupil diameter and amount of light entering eye
3. Secretes and reabsorbs aqueous humor
4. Controls shape of lens, part of focusing process
• Ciliary body – ring of smooth muscle connected to
ligaments that hold lens in place and epithelial cells that
secrete aqueous humor
© 2013 Pearson Education, Inc.
Wall of Eye – Neural Layer (9.10)
• Neural layer, or retina
• Innermost layer of eye
• Consists of:
• Thin outer layer (pigmented layer) that absorbs light
• Thick inner layer (neural layer) containing
photoreceptors, cells sensitive to light
© 2013 Pearson Education, Inc.
Layers of the eye wall
Fibrous Layer
Corneal Cornea
Sclera
limbus
Vascular Layer
Iris
Lens
Optic nerve
Ciliary body
Choroid
Neural Layer
Retina containing photoreceptors
© 2013 Pearson Education, Inc.
Figure 9.10 1 1
Eye Cavities (9.10)
• Ciliary body and lens divide eye into:
• Small anterior cavity
• Anterior chamber from cornea to iris
• Posterior chamber from iris to ciliary body and lens
• Large posterior cavity
• Taken up mostly by vitreous body or vitreous humor,
gelatinous substance
© 2013 Pearson Education, Inc.
Anterior and posterior cavities of the eye
Anterior Cavity
Cornea
Anterior chamber
Iris
Ciliary body
Lens
Posterior chamber
Posterior Cavity
Optic nerve
© 2013 Pearson Education, Inc.
Figure 9.10 2 2
Extrinsic Eye Muscles (9.10)
• Six extrinsic eye muscles position the eye
1. Superior oblique – controlled by cranial nerve IV
2. Superior rectus – controlled by cranial nerve III
3. Lateral rectus – controlled by cranial nerve VI
4. Inferior oblique – controlled by cranial nerve III
5. Inferior rectus – controlled by cranial nerve III
6. Medial rectus – controlled by cranial nerve III
© 2013 Pearson Education, Inc.
Lateral view of right eye showing extrinsic eye muscles
Superior oblique
Superior rectus
Levator
palpebrae
superioris
Optic nerve
Lateral rectus
Inferior oblique
Maxilla
Inferior rectus
© 2013 Pearson Education, Inc.
Figure 9.10 3 3
Medial view of right eye showing extrinsic eye muscles
Trochlea (ligamentous sling)
Superior rectus
Levator palpebrae superioris
Superior oblique
Optic nerve
Medial rectus
Inferior rectus
Inferior oblique
© 2013 Pearson Education, Inc.
Figure 9.10 4 4
Eye Movements (9.10)
• Each extrinsic muscle, when contracted, produces
different eye movements
1. Superior oblique – rolls eye; looks down and laterally
2. Superior rectus – eye looks up
3. Lateral rectus – eye looks laterally
4. Inferior oblique – rolls eye; looks up and laterally
5. Inferior rectus – eye looks down
6. Medial rectus – eye looks medially
© 2013 Pearson Education, Inc.
Anterior view of right eye showing movement of eye in response to extrinsic muscle contraction
Superior
rectus
Lateral
rectus
Trochlea
Superior oblique
Medial rectus
Inferior
oblique
Inferior rectus
© 2013 Pearson Education, Inc.
Figure 9.10
55
Module 9.10 Review
a. Name the three layers of the eye.
b. What gives the eyes their characteristic color?
c. Name the extrinsic eye muscles and describe the
way in which each moves the eye.
© 2013 Pearson Education, Inc.
Eye Anatomy Organization (9.11)
• Cornea – allows light entry into eye
• Dense matrix of multiple layers of collagen fibers
• No blood vessels, obtains nutrients from tears
• Lens
• Held in place by suspensory ligaments connected to ciliary
body
• Tension on ligaments keeps lens less than spherical
• Retina – contains photoreceptors, supporting cells,
neurons
• Choroid – contains nutrient-carrying blood vessels
• Sclera – dense, fibrous connective tissue
• Stabilizes shape of eye
• Insertion point for extrinsic eye muscles
© 2013 Pearson Education, Inc.
Visual Axis of the Eye (9.11)
• Light passes through center of cornea and center of lens to
specific location on retina
• Imaginary line from center of object seen through center of
cornea and lens to retina is visual axis
• Highest concentration of photoreceptors at center (fovea)
of an area (macula)
• Fovea is site of sharpest vision
• Optic nerve (CN II)
• Carries visual information to the brain
© 2013 Pearson Education, Inc.
Sectional view of both eyes
Transparent cornea
Lens
Suspensory ligaments
Ciliary body
Retina with photoreceptors
Vascular choroid layer
Sclera
Iris
Visual axis of
the eye
Lens
Choroid
Photoreceptors
in inner, neural
portion of retina
Nose
Sclera
Macula fovea
Optic nerve (N II)
© 2013 Pearson Education, Inc.
Orbital fat
Figure 9.11
11
Pupil Constriction and Dilation (9.11)
• Amount of light entering the eye controlled by two
layers of smooth muscles, located in iris
• Controlled by autonomic nervous system
• Pupillary dilator muscles
• Activated by sympathetic system and dim light
• Increase pupil diameter
• Pupillary constrictor muscles
• Activated by parasympathetic system and bright light
• Decrease pupil diameter
© 2013 Pearson Education, Inc.
Pupillary muscles of the iris respond to amount of light
Pupillary constrictor
(sphincter)
The pupillary dilator muscles
extend radially away from the
edge of the pupil. Contraction
of these muscles enlarges the
pupil.
Pupillary dilator
(radial)
Decreased light intensity
Increased sympathetic stimulation
© 2013 Pearson Education, Inc.
The pupillary constrictor muscles
form a series of concentric circles
around the pupil. When these
sphincter muscles contract, the
diameter of the pupil decreases.
Increased light intensity
Increased parasympathetic stimulation
Figure 9.11
22
Module 9.11 Review
a. Which eye structure does not contain blood
vessels?
b. List the structures and fluids that light passes
through from the cornea to the retina.
c. What happens to the pupils when light intensity
decreases?
© 2013 Pearson Education, Inc.
Light Refraction (9.12)
• Light refracted or bent when it passes from one
medium to another with different density
• For example, air to cornea
• Light rays refracted by cornea
• Additional refraction when light passes through
lens
• Lens provides refraction to focus light rays toward
focal point on retina
• Distance between lens and focal point is focal
distance
© 2013 Pearson Education, Inc.
Light rays are refracted to a focal point
Focal distance
Light
from
distant
source
(object)
Focal distance
Close
source
Focal
point
Lens
The closer the light source,
the longer the focal distance
Focal distance
© 2013 Pearson Education, Inc.
The rounder the lens,
the shorter the focal distance
Figure 9.12
11
Accommodation (9.12)
• Human lens can't move, but it can change shape, called
accommodation
• Close vision
• Ciliary muscles contract, moving ciliary body closer to lens
• Reduced tension on suspensory ligaments
• Elastic capsule of lens pulls lens into more spherical shape
• Thicker lens bends light rays more, so can focus on close
objects
• Distance vision
• Ciliary muscles relax, moving ciliary body away from lens
• Suspensory ligaments increase pull on lens
• Lens flattens
© 2013 Pearson Education, Inc.
Ciliary muscles control the shape of the lens
For Close Vision: Ciliary Muscle
Contracted, Lens Rounded
For Distant Vision: Ciliary
Muscle Relaxed, Lens Flattened
Focal point
on fovea
© 2013 Pearson Education, Inc.
Figure 9.12
22
Inverted and Reversed Images (9.12)
• Light from each point in an object focused on
retina
• Image on retina is inverted and reversed
• Brain compensates, so perception is of original
orientation
© 2013 Pearson Education, Inc.
Refraction makes images appear upside down and reversed on the retina
© 2013 Pearson Education, Inc.
Figure 9.12
33
Inner Limit of Clear Vision (9.12)
• To view closer objects requires greater thickening
of lens (more refraction)
• Limit to how close clear vision occurs (near point)
determined by elasticity of lens
• Children can focus 7–9 cm from eye
• With age, lens stiffens
• Young adult can focus 15–20 cm from eye
• Distance increases to 83 cm at age 60
© 2013 Pearson Education, Inc.
Module 9.12 Review
a. Define focal point.
b. When the ciliary muscles are relaxed, are you
viewing something close up or something in the
distance?
c. Why does the near point of vision typically
increase with age?
© 2013 Pearson Education, Inc.
Parts of the Retina (9.13)
• Pigmented part of retina
• Absorbs light that passes through neural part
• Prevents visual "echoes"
• Cells have biochemical reactions with retina's light receptors
• Neural part of retina
• Photoreceptors – in outermost layer, closest to pigmented
part
• Ganglion cells – form innermost layer of cells
• Optic disc – where axons of ganglion cells converge to form
optic nerve
• No photoreceptors, also called blind spot
© 2013 Pearson Education, Inc.
Parts of the retina
Pigmented Part of the Retina
Neural Part of the Retina
The outermost layer, closest to the
pigmented part of the retina,
contains the photoreceptors.
Ganglion cells form the
innermost layer of cells
in the neural part of the retina.
The axons of the ganglion cells
converge at the optic disc to form
the optic nerve, which carries visual
information to the brain. The optic
disc has no photoreceptors;
because an image falling on this
portion of the retina cannot be
detected, it is called the blind spot.
Central retinal vein
Central retinal artery
Optic nerve
Sclera
Choroid
© 2013 Pearson Education, Inc.
Blood vessels enter and leave the
interior of the eye within the optic
nerve. They radiate across the inner
surface of the eye, servicing the
inner layers of cells in the neural
part of the retina.
Figure 9.13 1 1
Photograph of retina in right eye
Optic disc
(blind spot)
Fovea (dense area at the
center of the lighter macula)
Macula
Central retinal artery and
vein emerging from center
of optic disc
© 2013 Pearson Education, Inc.
Figure 9.13 2 2
Photoreceptors of the Retina (9.13)
• Rods – black and white vision
• Highly sensitive, enable us to see in dim light
• About 125 million in each eye
• Highest density at periphery of retina
• Cones – color vision
• Sharper, clearer vision than rods but require more light
• About 6 million in each eye
• Highest density at fovea of macula
• Bipolar cells – not photoreceptors, but are connection
between rods and cones and ganglion cells
© 2013 Pearson Education, Inc.
Photoreceptors of the retina
Pigmented part of retina
Photoreceptors of the
Retina
Rods
Cones
Other retinal cells
can facilitate or
inhibit communication between
photoreceptors
and ganglion cells
Bipolar cells
Ganglion cells
LIGHT
© 2013 Pearson Education, Inc.
Figure 9.13 3 3
Module 9.13 Review
a. Define rods and cones and briefly state their
functions.
b. If you enter a dimly lit room, will you be able to
see clearly? Why or why not?
c. If you had been born without cones in your eyes,
explain why you would or would not be able to
see.
© 2013 Pearson Education, Inc.
Photoreceptor Structures (9.14)
• Rods and cones have two segments
1. Outer segment – contains flattened membranous plates, discs
• Discs contain special organic compounds, visual pigments
• Pigments derivatives of rhodopsin, pigment found in rods
• Rhodopsin composed of opsin and retinal (synthesized
from vitamin A)
• Type of opsin determines wavelengths absorbed by retinal
2. Inner segment – contains major organelles
• Responsible for cell functions other than photoreception
(responding to photons)
© 2013 Pearson Education, Inc.
Rods and cones structure
Structure of
Cones
Structure of Rods
Pigment
Epithelium
In a cone, the discs are infoldings
of the plasma membrane, and the
outer segment tapers to a blunt
point.
In a rod, each disc is an
independent entity, and the outer
segment forms an elongated
cylinder.
Melanin
granules
Outer Segment
Discs
Connecting
stalks
Inner Segment
Mitochondria
Golgi
apparatus
Nuclei
Cone
Rhodopsin
molecule
Retinal
Opsin
Rods
Each photoreceptor
synapses with a bipolar
cell.
Bipolar cell
LIGHT
© 2013 Pearson Education, Inc.
Figure 9.14 1 1 – 22
Light Energy to Nerve Impulse (9.14)
• Light strikes visual pigment
• Retinal molecule changes shape
• Changes permeability of outer segment
• Converts light energy into nerve impulse
© 2013 Pearson Education, Inc.
Changes in visual pigments with exposure to light
1
When light is absorbed,
retinal changes to a more
linear shape. This change
activates the opsin molecule.
2
Opsin activation changes
the rate of neurotransmitter
release by the inner
segment at its synapse
with a bipolar cell.
Photon
6
Once the retinal has
returned to its original
shape, it can recombine with
opsin. The rhodopsin
molecule is now ready to
repeat the cycle. The
regeneration process takes
time; after exposure to very
bright light, photoreceptors
are inactivated while pigment
regeneration is under way.
3
enzyme
Opsin
Opsin
Changes in
bipolar cell
activity are
detected by
one or more
ganglion cells.
Neurotransmitter
release
Bipolar
cell
4
5
The retinal is converted
to its original shape.
This conversion
requires energy in the
form of ATP.
© 2013 Pearson Education, Inc.
After absorbing a
photon, the rhodopsin
molecule begins to
break down into retinal
and opsin, a process
known as bleaching.
Ganglion
cell
Figure 9.14
33
Wavelengths of Light (9.14)
• Three types of cones, each with different type of opsin
sensitive to different wavelengths of light
• Can be stimulated in various combinations to perceive
colors, stimulation of all three equally is perceived as white
1. Blue cones – 16 percent of cones
2. Green cones – 10 percent of cones
3. Red cones – 74 percent of cones
• Color blindness comes from lacking one or more cone
pigments
• 2 percent of males lack either red or green pigments
© 2013 Pearson Education, Inc.
Wavelengths of light to which types of cones respond
Light absorption
(percent of maximum)
100
75
Blue
cones
Rods
Red
cones
50
25
0
Green
cones
WAVELENGTH (nm)
650
500
550
600
400
450
Violet Blue
Green Yellow Orange
© 2013 Pearson Education, Inc.
700
Red
Figure 9.14
44
Module 9.14 Review
a. Identify the three types of cones.
b. Explain why your vision is momentarily impaired
after viewing a camera's flash.
c. How could a diet deficient in vitamin A affect
vision?
© 2013 Pearson Education, Inc.
Depth Perception (9.15)
• Images from left and right eyes overlap
• Visual cortex of each cerebral hemisphere
receives information from both eyes
• Depth perception is interpretation of threedimensional relationships among objects
• Brain does this by comparing relative positions of
objects in images received by two eyes
© 2013 Pearson Education, Inc.
Visual pathways and depth perception
Combined Visual Field
Left side
Right side
Left eye Binocular vision Right eye
only
only
The Visual Pathways
Photoreceptors in the retina
Retina
Optic disc
Optic nerve (N II)
Optic chiasm
Optic tract
Optic tract
Lateral geniculate nucleus
Lateral geniculate
nucleus (thalamus)
Visual cortex of cerebral hemispheres
Optic radiation
Left cerebral
hemisphere
© 2013 Pearson Education, Inc.
Right cerebral
hemisphere
Figure 9.15
11
Module 9.15 Review
a. Define optic radiation.
b. Where are visual images perceived?
c. Trace the visual pathway, beginning at the
photoreceptors in the retina.
© 2013 Pearson Education, Inc.
Accommodation Problems (9.16)
• Emmetropia or normal vision
• Distant objects focused clearly when ciliary muscles
relaxed and lens flattened
• Myopia or nearsighted (can see close objects most
clearly)
• Eyeball too deep or curvature of lens too great
• Image of distant object focused in front of retina
• Corrected with diverging lens to spread light rays apart
© 2013 Pearson Education, Inc.
Accommodation Problems (9.16)
• Hyperopia or farsighted (can see distant objects most
clearly)
• Eyeball too shallow or lens too flat
• Ciliary muscles have to contract to focus on distant
object
• Close range, lens cannot refract enough
• Corrected with converging lens for additional refraction
© 2013 Pearson Education, Inc.
Accommodation issues with the eye
Emmetropia
Myopia
Diverging
lens
Hyperopia
Converging
lens
© 2013 Pearson Education, Inc.
Figure 9.16
11
Reshaping the Cornea (9.16)
• One way to correct myopia and hyperopia is by surgery reshaping
cornea
• Photorefractive keratectomy (PRK)
• Uses computer-guided laser to remove 10–20 µm of cornea from
outer surface
• Laser-assisted in-situ keratomileusis (LASIK)
• Reshapes interior layers of cornea, covers with flap of normal
cornea
• 70 percent LASIK patients achieve normal vision
• Corneal scarring rare in either procedure
© 2013 Pearson Education, Inc.
Surgical reshaping of cornea
© 2013 Pearson Education, Inc.
Figure 9.16
11
Module 9.16 Review
a. Define emmetropia.
b. Discuss two surgical procedures for correcting
myopia and hyperopia.
c. Which type of lens would correct hyperopia?
© 2013 Pearson Education, Inc.
Disorders of Olfaction (9.17)
• Disorders of olfaction (sense of smell) result from:
• Head injury that damages olfactory nerve
• Normal age-related changes
• Olfactory receptors regularly replaced by stem cell
division
• But total number declines with age and receptors become
less sensitive
© 2013 Pearson Education, Inc.
Disorders of Gustation (9.17)
• Disorders of gustation (sense of taste) result from:
• Problems with olfactory receptors
• Sense of smell and taste closely related
• Common cold affects both
• Damage to taste buds – by inflammation or infections
• Damage to cranial nerves (VII, IX, X)
• Age-related changes
© 2013 Pearson Education, Inc.
Disorders of Vision (9.17)
• Cataract
• Condition in which lens loses transparency
• Can result from injury, radiation, reaction to drugs
• Most common form is senile cataracts
• Natural consequence of aging
• Damaged or nonfunctional lens can be replaced by
artificial substitute
© 2013 Pearson Education, Inc.
Cataracts
Normal eye
Eye with
cataract
© 2013 Pearson Education, Inc.
Figure 9.17
33
Equilibrium Disorders (9.17)
• Vertigo – illusion of movement
• Caused by conditions altering function of:
• Internal ear receptor complex
• Examples:
• Anything that disturbs endolymph, like flushing external
acoustic meatus with cold water
• Excessive consumption of alcohol or certain drugs
• Vestibular branch of vestibulocochlear nerve
• Sensory nuclei and pathways in central nervous system
• Motion sickness – headache, sweating, nausea, vomiting
• Motion sickness drugs depress activity in brain stem
© 2013 Pearson Education, Inc.
Hearing Disorders (9.17)
• Conductive deafness
• From interference with normal transfer of vibrations from
tympanic membrane to oval window
• Caused by excess wax, trapped water, scarring of tympanic
membrane, immobilization of auditory ossicles
• Nerve deafness
• Problem with cochlea or along auditory pathway
• Can be caused by very loud noises damaging sensory cilia on
receptor cells
• Bacterial or viral infections can also kill receptor cells
© 2013 Pearson Education, Inc.
Hearing Loss (9.17)
• Occurs with age from:
• Accumulated damage from loud noises and other
injuries
• Decreasing flexibility of tympanic membrane
• Stiffness of auditory ossicle joints and ossification of
round window
© 2013 Pearson Education, Inc.
Changes in hearing with age
© 2013 Pearson Education, Inc.
Figure 9.17
55
Module 9.17 Review
a. Which cranial nerves provide taste sensations
from the tongue?
b. Identify two common classes of hearing-related
disorders.
c. What causes vertigo?
© 2013 Pearson Education, Inc.